Vesicular imaging process

ABSTRACT

A vesicular imaging method is employed wherein a poly(alkyl acrylate) or a poly(alkyl carbamate) produces a gas upon exposure to actinic light enabling the production of a visible image in the exposed areas of a vesicle-retaining film upon development.

o 111mm Staios 1151 3,635,768 Monahan 1 Jan, 118, 1972.

{54] VESICULAR IMAGING PROCESS 3,032,414 5/1962 James et a1... ..96/49 x I 3,091,532 5/1963 Michaelsen. ..96/48 [72] Inventor. Alan R. Monahan, East Rochester, NY. 3l43418 8/1964 Priest et all 1 l l I I t I "96/91 X [73] Assignee: Xerox Corporation, Rochester, NY. 3,183,091 5/1965 Sporer et a1. 3,260,599 7/1966 Lokken [22] 1969 3,281,240 10/1966 Cassiers et 51.. [21] Appl. No.: 811,672 3,291,600 12/1966 Nicol! 3,298,833 1/1967 Gaynor.... Rem"! APPIICQM" 19m 3,355,295 1 H1967 Pnest ..96/91 [63] Continuation-impart of Ser. No. 553,040, May 26,

I966 abandonei Primary Examiner-Charles L. Bowers, Jr.

Attorney-James J. Ralabate and Dav/id C. Petre [52] U.S.Cl ..96/27,96/48,96/l15 51] 1111. C1. ....G03c 5/04, 003C 5/24 AB TRA T [58] F1eld of Search ..96/9l, 91 D, 498621.151; A vesicular imaging method is employed wherein a polywlky] acrylate) or a poly(alkyl carbamate) produces a gas upon ex- [56] References Cited osuroto act1n1c hght enablmg the productron of a v1s1b1e 1mage 1n the exposed areas of a veslcle-retalmng film upon UNITED STATES PATENTS development- 2,703,756 3/1955 Herrick et a1 ..96/49 21 Claims, No Drawings VESICUILAR IMAGING PROCESS CROSS REFERENCES TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION This invention relates to imaging systems and, more specifically, systems in which lightscattering vesicular areas are formed in an imagable plate in image configuration.

Several light-scattering imaging systems have been recently developed. Typical of these are the relief" system described, for example, in U.S. Pat. Nos. 3,055,006 and 3,111,179 and the frost system described, for example, in U.S. Pat. Nos. 3,055,006 and 3,113,179.1n each of these systems, an electrostatic latent image is formed on the surface of a suitable heatdeformable thermoplastic material. When developed in the relief process, the surface of the thermoplastic deforms along the edges of the charged areas producing a line image. When developed according to the frost process, a series of small surface folds or wrinkles having the appearance of frost appears across the charged areas giving solid image area coverage. In each case, the image is visible due to light scattered by the surface deformations.

In another light-scattering imaging process, exemplified by the processes disclosed in U.S. Pat. Nos. 3,081,169 and 3,037,862, a transparent binder contains a light-sensitive ingredient. This ingredient, typically a diazonium salt, decomposes upon exposure to suitable radiation, forming gas molecules. The sheet is then heated to provide mobility and coalescence forming a plurality of small light-scattering bubbles throughout image areas.

The above light-scattering imaging systems are suitable for many uses. In general, they produce images of unusually high resolution. However, each system has disadvantages which have prevented wide commercial use. The surface deformation systems tend to be adversely affected by surface contamination present on the deformable sheets before imaging. Also, materials which deform easily to form images tend to be soft and tacky and subject to damage after imaging. The images are often of low contrast and, especially relief images, may require complex viewing systems such as Schlerian projection systems.

The vesicular imaging systems also suffer from materials limitations. The photosensitive agent must be uniformly dispersed throughout the binder to insure image uniformity. Binders must be selected in which the photosensitive agent may be easily dispersed and which do not interfere with the decomposition or reaction. A further limitation is placed on the binder material by the high-temperature requirements of the development step which generally requires heating the film for a short period to a temperature of 200 F. or substantially above. The degree of permanence of vesiscular imaged sheets may not be sufficient for some uses since the photosensitive agent remains in unexposed areas and may be sensitive to heat and/or moisture.

Thus, there is a continuing need for improved light-scattering-type imaging systems and improved materials for use in such systems.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a lightscattering imaging system which overcomes the above-noted disadvantages.

It is another object of this invention to provide an improved vesicular light-scattering imaging system.

It is another object of this invention to provide, in some embodiments, a single component imaging system.

It is another object of this invention to provide a single component polymeric vesicular imaging system.

The above objects and others are obtained by providing a system using films comprising compositions having the general formula R; where R is selected from the group consisting of radicals having the general formulas:

wherein X is an aliphatic radical, which may be substituted and which has two to eight carbon atoms and Z is selected from the group consisting of 0, oxygen and S, sulphur; and methods of imaging said films to form vesicular images by exposing the films to activating electromagnetic radiation and softening.

Compositions of the general formula R can be an appendage off any film-forming backbone or any of the three radicals can be synthesized as the polymer backbone itself. Where a composition of the general formula R is an appendage of a filmforming backbone, nondecomposable backbones having the general formula I i CH2-(|JH] wherein n is a positive integer of at least 2; and

Y is selected from the group consisting of H, Ch and C H are preferred in the aspect that the film remains polymeric in nature in both imaged and nonimage-d areas and, therefore, substantially retains its original strength across the sheet. As is further pointed out in the examples, this is an ideal situation since the gas-forming reaction does not degrade the polymer to a monomer and thereby weaken the film. However, when Y in the above general formula is a methyl or an ethyl group, a photolytic reaction to monomer does occur. But since this is a very slow reaction, the depolymerization is not detrimental to the imaging characteristics of this class of polymers. The most highly photosensitive materials within the compositions of the above general formula have been found to be poly(t-butyl acrylate) and poly(t-butyl-N-vinyl-carbamate). These, therefore, are preferred materials.

Preferred compositions having the general formula R have the general formula where Z is selected from the group consisting of O and 8. These compositions have high sensitivity, apparently because of the high number of acidic protons. These compositions may be an appendage off any film-forming backbone or may be a major portion of the polymer backbone, for example as a result of the repeating unit The compositions of the above general formula are formed into a continuous film (or dispersed as fine particles in a thermoplastic binder or mixed with a lower melting resin), exposed to an image of activating electromagnetic radiation preferably ultraviolet radiation, whereby a latent image made up of gas molecules is formed in the film. The film is softened to produce bubbles, and render the image visible. It will be ap preciated that other radiation such as lower wavelength electromagnetic radiation, for example, X-rays may also be used, but ultraviolet radiation is preferred because of the ready availability of UV sources and because the films hereof are more sensitive to UV.

Softening relieves the microscopic stress induced in the polymer matrix by the gaseous decomposition product. The stress is transformed into a bubble (vesicle) which reorients the crystalline portions of the polymer into an opaque image area. Any suitable softening technique may be used including heat softening, solvent vapor softening or contacting the film with a liquid that swells and softens the film. Because it is dry, simple and produces excellent images, heat softening is preferred herein.

it will be appreciated that there need be no separate softening step if the film is already sufficiently soft (for example, due to the presence of a film-forming solvent in a freshly made film) during the exposure step.

In heat softening it has been found to be preferred in order to optimize the bubble-forming image effect hereof to heat the film to at least about its softening or melting temperature.

The imagable films hereof may be prepared as a self-supporting polymeric film or may be coated on any suitable substrate. Substrate materials include conductors such as metals, transparent materials such as polyethylene terephthalate, polyvinylidine chloride, glass, etc., and opaque insulating materials such as paper. Since the light-struck areas will appear white by reflected light, the film may be coated onto a black background to produce a positive-appearing final image. Where the film is used as a self-supporting or composite transparency, (for example where the film is on a transparent substrate) the image when projected will appear as a negative in that nonlight-struck areas will be transparent and light-struck areas will be light scattering and appear opaque on the film.

The thickness of the films herein is not critical but are generally greater than about 1 micron because of fabrication problems for submicron films. Thicknesses up to about a mil are suitable for transparency projection of the imaged film and still thicker films are satisfactory where the imaged film is to be used as a directly viewable image.

Where R is an appendage of film-forming backbone having as previously described, it appears that in the case of the polyesters the radical indicated at X in a previously defined general formula containing X is removed by photolysis leaving poly(acrylic acid) or poly(methacrylic acid). Where the amine group is present between the polymer chain and the ester group, carbon dioxide and an alkene group formed from the radical indicated at X in a previously defined general formula containing X" are broken off, leaving poly(ethyleneamine). The mechanism of the photolysis of a typical polymer, poly(t-butyl acrylate), within the above described general formula is believed to be as follows:

As can be seen from the photolysis of poly(t-butyl acrylate) the presence of a beta carbon in the ester is critical for the above-indicated reaction to take place. In this instance, isobutene gas molecules are formed during photolysis. These may be formed into expanded bubbles by heating the polymer to its softening temperature.

The rate of gas formation has been found to be autoaccelerated when a minimum of one acrylic acid unit is generated per chain. That gain is obtained in this system is surprising and not fully understood at this time. However, gain is specially advantageous since it markedly increases the photographic speed of the imaging material.

It is not unreasonable to assume that the autocatalysis is due to a cooperative mechanism between acid and ester, i.e.,

CH2 CH;

The ease with which the acidic proton now tends to be liberated is much more rapid than the photolysis of single isolated units. A mechanism of this type would tend to propagate down the polymeric chain giving isobutene yields comparable to chain lengths.

The speed of this vesicular imaging process is extremely dependent on the spatial conformation of the ester (E) with respect to the carbonyl, i.e.,

The rate of elimination of olefin has been found to be approximately seven to eight times faster from conformation A than from conformation B.

The invention will be further understood upon reference to the following examples which describe methods of imaging according to the process of this invention. All parts and percentages are by weight unless otherwise indicated. The following examples constitute preferred embodiments of the process of this invention.

EXAMPLE I About 30 parts of poly(t-butyl acrylate), available from Borden Chemical Co., is dissolved in about parts toluene. A film of this solution is cast onto a glass substrate by means of a drawdown bar. The film is dried in an oven for about24 hours at about 50 C. under vacuum. The dry film thickness is about 10 microns. The resulting plate is exposed to a blackand-white test pattern in the form of a chrome pattern on quartz. Exposure is by means of a l-lanovia 83A-l low-pressure mercury lamp having about 88 percent ultraviolet output at 2,537 angstroms. The plate is exposed for about 1 minute, total exposure being about 10 quanta/emf. The plate is then heated to the softening temperature of the polymer, about 200 C. An image corresponding to a negative of the original is observed in the plate. This image consists of a plurality of small light-scattering bubbles throughout the image area. Average size of individual bubbles is about 0.5 microns.

EXAMPLE ll About 30 parts of poly(ethyl acrylate) is dissolved in about 100 parts cyclohexane. A film is cast onto a glass substrate by means of a drawdown bar to a dry thickness of about 20 microns. The plate is dried in an oven for about 24 hours at about 50 C. under vacuum. The plate is exposed by means of ultraviolet light as in example 1 except that exposure here is for about 2 minutes. The plate is heated to about the melting temperature of the polymer, about 70 C. An image conforming to a negative of the original is formed with a plurality of small bubbles dispersed throughout image areas.

EXAMPLE III A plate is prepared as in example I except that the substrate is black paper instead of glass. The plate is exposed to ultraviolet radiation as in example I. The plate is heated to the softening temperature of the polymer about 200 C. A negative image consisting of a plurality of small bubbles dispersed throughout image areas is observed. Since the vesicular areas arelight scattering they appear white and block the black substrate. The black substratethus can be observed through positive image areas giving the appearance of a black-on-white positive image conforming to the original.

EXAMPLE IV A poly(t-butyl-N-vinyl-carbamate) resin is prepared by the method described by R. Hart in Makromol Chem., Vol. 32, page 51 (1959). About 30 parts of this polymer is dissolved in about 100 parts toluene. The solution is cast onto a glass substrate by means of a drawdown bar. The film is dried in an oven for about 24 hours at about 50 C. under vacuum. The dry film thickness is about 20 microns. The plate is exposed to a black-and-white test pattern by means of a Hanovia 93A-1 low-pressure mercury lamp, having primary output at 2,537 and 1,849 angstroms. Total exposure is about quanta/cm The plate is then heated to the softening temperature of the polymer, about 250 C. An excellent image conforming to a negative of the original with a plurality of light-scattering bubbles dispersed throughout negative image areas is observed. Positive areas of the image have a slight pink color characteristic of the polymer.

EXAMPLE V About 10 parts poly decamethylene sebacate and about 6 parts poly(t-butyl acrylate) are dissolved in about 100 parts toluene. The solution is cast onto a glass substrate to a dry thickness to about microns. the plate is exposed to a lightand-shadow pattern by means of ultraviolet radiation as described in example 1, except that the exposure is for about 2 minutes. The plate is then heated to about 75 (3., the melting pointof the poly decamethylene sebacate. An excellent image corresponding to a negative of the original is observed, consisting of a plurality of light-scattering bubbles dispersed throughout negative image areas.

EXAMPLE VI A plate is prepared as in example V. The plate is placed on a platen heated to about 75 C., the melting point of the poly decamethylene sebacate. While at this temperature, the plate is exposed to a light-and-shadow pattern by means of ultraviolet radiation as described in example V. An image is seen to develop consisting of a plurality of light-scattering bubbles dispersed throughout exposed image areas. The plate is then removed from the heated platen and cooled to room temperature. An excellent image corresponding to a negative of the original results.

EXAMPLE VII A sample of poly(t-butyl acrylate) is placed in a ball mill and milled to an average particle size of about 1 micron. About 10 parts of this powdered resin is dispersed in about 10 parts molten polystyrene. The dispersion is cast onto an aluminum substrate to a thickness of about 15 microns and solidified. The plate is exposed to a light-and-shadow pattern by means of ultraviolet radiation as described in example 1, except that the exposure is for about 3 minutes. The plate is then heated to about 175 C., the melting point of the polystyrene resin. A good image corresponding to a negative of the original results, consisting of a plurality of fine bubbles uniformly dispersed throughout exposed image areas.

EXAMPLE VIII About 30 parts of poly(t-butyl acrylate) is dissolved in about parts cyclohexane. A film of this solution is cast onto a glass substrate by means of a drawdown bar to a dry thickness of about 100 microns. The film is stripped from the glass substrate and placed in a frame. The film is self-supporting. The plate is exposed to a black-and-white test pattern as in example I. Total exposure time is about 2 minutes. The film is placed in contact with a smooth metal platen, which will not adhere to the softened polymer, and heated to a temperature of about 200 C., the softening temperature of the polymer. A bubble image corresponding to the original is observed in the film. The film is then cooled to room temperature and removed from the platen. A negative image results which when projected by conventional projection means appears as a negative of the original, the unexposed areas passing light to the screen and the light-scattering exposed areas appearing black on the screen.

EXAMPLE IX About 30 parts of poly( n-propyl ethyl acrylate) is dissolved in about 100 parts cyclohexane. A film is cast and dried as in example II. The plate is exposedand heated as in example 11. An imaged member conforming to a negative of the original, when the imaged member is used as a projection transparency, is formed with a plurality of small bubbles dispersed throughout the imagewise exposed areas.

EXAMPLE X About 5 parts of poly(a-chloroethyl acrylate) is dissolved in about 100 parts toluene. A film is cast and dried as in example II to form about a l-micron layer. The plate is exposed as in example II. The plate is heated to about the melting temperature of the polymer, about C. An image is produced as in example IX.

EXAMPLE X] About 25 parts of the poly tertiary butyl ester of 2-keto-3- methyl'3-butenoic acid is dissolved in about 100 parts acetone. A film is cast and dried as in example II to form about a 10-micron layer. The plate is exposed by means of ultraviolet light as in example I except that the exposure is for about 5 minutes. The plate is heated to about the melting temperature of the polymer, about 200 C. An image is formed as in example IX.

EXAMPLE XII About 10 parts of the this ester of poly(t-butyl acrylate) is dissolved in about 100 parts chloroform. A film is cast and dried as in example II to form about a 2-micron layer. The plate is exposed by means of ultraviolet light as in example 1 except that the exposure is for about 3 minutes. The plate is heated to about the melting temperature of the polymer, about 180 C. An imaged member as inexample IX is formed.

EXAMPLE XIII About 30 parts of poly(carbonyl oxy isobutylene) is dissolved in about 100 parts dimethylbromide. A film is cast and dried as in example II to form about a lO-micron layer. The plate is exposed by means of ultraviolet light as in example I except that the exposure is for about 7' minutes. The plate is heated to about the melting temperature of the polymer, about 200 C. An imaged member as in example 1X is formed.

EXAMPLE XIV About 8 parts of poly(thio carbonyl oxy isobutylene) is dis solved in about 100 parts toluene. A film is cast and dried as in example II to form about a 1.5-micron layer. The plate is ex posed by means of ultraviolet light as in example 11. The plate is heated to about the melting temperature of the polymer, about 250 C. An imaged member as in example IX results.

About 15 parts of poly(isopropyl carbamate) is dissolved in about 100 parts methanol. A film is cast and dried as example ll to form a dried film thickness of about 4 microns. The plate is exposed by means of ultraviolet light as in example 1 except that the exposure is for about 10 minutes. The plate is heated to about the melting temperature of the polymer, about 225 C. An imaged member as in example lX results.

Although specific materials and conditions are set forth in the above examples, these were merely illustrative of the present invention. Various other compositions, such as the typical materials listed above and various conditions, where suitable, may be substituted for those given in the examples with similar results. The photosensitive resin layer of this invention may have other materials, presently known or discovered in the future, mixed therewith to enhance, to sensitize, synergize or otherwise modify its properties. For example, colorants may be added to the layer so as to give color to the transparent, nonexposed areas. The photosensitive layer may be sensitized, if desired, to make it sensitive to visible light or other portions of the electromagnetic spectrum. However, a fixing step is then preferably included to make the imaged film insensitive to light during viewing.

Many other modifications of the present invention will occur to those skilled in the art upon a reading of this disclosure. These are intended to be encompassed within the spirit of this invention.

What is claimed is:

l. Avesicular imaging method comprising the steps of:

a. exposing to actinic radiation to produce a gas, a vesicleretaining film consisting essentially of a poly(alkyl acrylate) represented by the formula where Y is selected from the group consisting of H, Ch and C H Z is selected from the group consisting of oxygen and sulfur; X is an alkyl group having from two to eight carbon atoms inclusive which can be further substituted by a chlorine atom, and n is a positive integer greater than 1 as the sole gasforming material, and;

b. softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.

2. A vesicular imaging method comprising the steps of:

a. exposing to actinic radiation to produce a gas a vesicleretaining film consisting essentially of a poly(alkyl acrylate) represented by the formula:

X n wherein Y is selected from the group consisting of H, CH and C 11 X is an alkyl group having from two to eight carbon atoms inclusive which can be further substituted by a chlorine atom and n is a positive integer greater than 1 as the sole gasforming material, and;

b. softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.

3. The method of claim 2 wherein said film resides porting substrate.

4. The method of claim 2 wherein said film is self-supportmg.

5. The method of claim 2 wherein the film material comprises a thermoplastic binder having dispersed therein at least one of said poly(alkyl acrylates).

6. The method of claim 2 wherein Y is CH 7. The method of claim 2 wherein Y is C l-l 8. The method of claim 2 wherein X is an alkyl group having two carbon atoms.

9. The method of claim 2 wherein X is an alkyl group having four carbon atoms.

10. The method of claim 9 wherein X is a t-butyl group.

1 1. The method of claim 2 wherein X is an ethyl group.

12. The method of claim 10 wherein said film is self-supporting.

13. The method of claim 2 wherein X is an n-propyl ethyl acrylate group.

14. The method of claim 5 wherein X is a t-butyl group and said poly( alkyl acrylate) is dispersed in decamethylene sebacate.

15. The method of claim 2 wherein said exposure and softening occurs simultaneously.

16. The method of claim 14 wherein said exposure and said softening takes place simultaneously.

17. The method of claim 2 wherein X is a t-butyl group and said poly(alkyl acrylate) is dispersed in a polystyrene binder.

18. A vesicular imaging method which comprises:

a. exposing to actinic radiation to produce a gas a vesicleretaining film material comprising as the gas-forming material poly(t-butyl-N-vinyl-carbamate) resin and;

b. softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.

19. An imaging method which comprises exposing to actinic radiation to produce a gas a vesicle-retaining film material comprising as the gas-forming material poly(isopropyl carbamate) and softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.

20. A vesicular imaging method which comprises exposing to actinic radiation to produce a gas a vesicle-retaining film material consisting essentially of a poly(alkyl acrylate) represented by the formula:

on a supwherein Y is selected from the group consisting of H, CH and C H X is an alkyl group having from two to eight carbon atoms inclusive which can be further substituted by a chlorine atoms, and n is a positive integer greater than 1 as the sole gasforming material, while simultaneously softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.

21. The method of claim 19 wherein said exposure and said softening occur simultaneously. 

2. A vesicular imaging method comprising the steps of: a. exposing to actinic radiation to produce a gas a vesicle-retaining film consisting essentially of a poly(alkyl acrylate) represented by the formula:
 3. The method of claim 2 wherein said film resides on a supporting substrate.
 4. The method of claim 2 wherein said film is self-supporting.
 5. The method of claim 2 wherein the film material comprises a thermoplastic binder having dispersed therein at least one of said poly(alkyl acrylates).
 6. The method of claim 2 wherein Y is CH3.
 7. The method of claim 2 wherein Y is C2H5.
 8. The method of claim 2 wherein X is an alkyl group having two carbon atoms.
 9. The method of claim 2 wherein X is an alkyl group having four carbon atoms.
 10. The method of claim 9 wherein X is a t-butyl group.
 11. The method of claim 2 wherein X is an ethyl group.
 12. The method of claim 10 wherein said film is self-supporting.
 13. The method of claim 2 wherein X is an n-propyl ethyl acrylate group.
 14. The method of claim 5 wherein X is a t-butyl group and said poly(alkyl acrylate) is dispersed in decamethylene sebacate.
 15. The method of claim 2 wherein said exposure and softening occurs simultaneously.
 16. The method of claim 14 wherein said exposure and said softening takes place simultaneously.
 17. The method of claim 2 wherein X is a t-butyl group and said poly(alkyl acrylate) is dispersed in a polystyrene binder.
 18. A vesicular imaging method which comprises: a. exposing to actinic radiation to produce a gas a vesicle-retaining film material comprising as the gas-forming material poly(t-butyl-N-vinyl-carbamate) resin and; b. softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.
 19. An imaging method which comprises exposing to actinic radiation to produce a gas a vesicle-retaining film material comprising as the gas-forming material poly(isopropyl carbamate) and softening said film whereby said gas produces vesicles in the exposed areas of said film thereby producing a visible image.
 20. A vesicular imaging method which comprises exposing to actinic radiation to produce a gas a vesicle-retaining film material consisting essentially of a poly(alkyl acrylate) represented by the formula:
 21. The method of claim 19 wherein said exposure and said softening occur simultaneously. 